1. Field of the Invention
The present invention relates to a thin film magnetic head comprising a magnetoresistive element exhibiting magnetoresistance, and a substrate comprising a monitor element used in a step before the thin film magnetic head is manufactured. Particularly, the present invention relates to a thin film magnetic head which can decrease the occurrence of smearing in order to comply with the demand for gap narrowing accompanying an increase in recording density in future, and a substrate for forming the thin film magnetic head thereon.
2. Description of the Related Art
FIG. 5 is a partial plan view of a substrate on which a conventional thin film magnetic head is formed, and FIG. 6 is a sectional view taken along line VIxe2x80x94VI in FIG. 5. In FIG. 5, an upper gap layer 11 and an upper shielding layer 12 are not shown.
As shown in FIG. 6, a lower shielding layer 3 made of a magnetic material such as a NiFe alloy or the like is formed on a substrate 1 comprising, for example, Al2O3xe2x80x94TiC (alumina-titanium carbide), and a lower gap layer 4 made of an insulating material such as Al2O3 or the like is further formed on the lower shielding layer 3.
Referring to FIG. 6, a plurality of magnetoresistive elements 13 and a monitor element 5 are formed in a line in the ABS direction (the X direction shown in the drawing) on the lower gap layer 4.
Furthermore, a multilayer film 7 comprising, for example, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a spin-valve film (a GMR element) comprising a free magnetic layer is formed at the center of each of the magnetoresistive elements 13. The spin-valve film serves as an element which utilizes magnetoresistance so that the electric resistance changes with a change in a leakage magnetic field from a recording medium to detect a recording signal. As shown in FIG. 6, electrode layers 8 made of a nonmagnetic metal material such as Cr (chromium) or the like are formed on both sides of the multilayer film 7.
The monitor element 5 also has the same structure as the magnetoresistive elements 13. Namely, a multilayer film 9 exhibiting magnetoresistance is formed at the center of the monitor element 5, and electrode layers 10 made of Cr (chromium) or the like are formed on both sides of the multilayer film 9. The magnetoresistive elements 13 and the monitor element 5 are simultaneously formed in a pattern on the lower gap layer 4.
As shown in FIG. 5, a pair of the electrode layers 8 constituting each of the magnetoresistive element 13, and a pair of the electrode layers 10 constituting the monitor element 5 are formed symmetrically on both sides of the multilayer films 7 and 9, respectively. The electrode layers 8 and 10 are exposed from the ABS.
As shown in FIG. 5, in the electrode layers 8 or 10 formed on both sides of each of the multilayer film 7 or 9 exposed from the ABS, the width dimension from one of the electrodes layers 8 or 10 to the other is T1. For example, the width dimension T1 is conventionally 80 xcexcm or more.
As shown in FIG. 6, an upper gap layer 11 made of an insulating material such as Al2O3 or the like is formed on the magnetoresistive elements 13 and the monitor element 5, and an upper shielding layer 12 made of a NiFe alloy (permalloy) or the like is further formed on the upper gap layer 11.
The length dimension from the lower gap layer 4 to the upper gap layer 11 is defined as a magnetic gap G1.
The monitor element 5 serves as a processing monitor provided for setting the DC resistance (DCR) of each of the plurality of magnetoresistive elements 13, which are formed in the same line as the monitor element 5, to a predetermined value. After the monitor element 5 plays the role as the processing monitor, the monitor element is removed.
In order to set the DC resistance (DCR) of each of the magnetoresistive elements 13 to the predetermined value, the ABS-side surfaces (refer to FIG. 5) of the magnetoresistive elements 13 and the monitor element 5 are ground (height controlling) while measuring the DC resistance between the electrode layers 10 constituting the monitor element 5. Once a predetermined DC resistance value is obtained, grinding of the ABS side is finished.
Since the plurality of magnetoresistive elements 13 have the same structure and are formed in a line parallel to the ABS, as described above, when the DC resistance of the monitor element 5 reaches a predetermined value by grinding, the DC resistance value of each of the magnetoresistive elements 13 also reaches the predetermined value.
However, the gap is narrowed accompanying an increase in the recording density, and thus in grinding the ABS-side surfaces of the magnetoresistive elements 13 and the monitor element 5 while measuring the DC resistance between the electrode layers 10 constituting the monitor element 5, smearing occurs between the shielding layers 3 and 12 and the electrode layers 10 of the monitor element 5, which are exposed from the ABS, to cause a problem in which the electrode layers 10 are electrically connected to the shielding layers 3 and 12. Therefore, the DC resistance (DCR) between the electrode layers 10 of the monitor element 5 cannot be precisely measured, and thus the length dimension of the magnetoresistive elements 13 in the height direction (the Y direction shown in the drawing) cannot be set to a value with which the predetermined resistance value is obtained.
The smearing also occurs between the electrode layers 8 of each of the magnetoresistive elements 13 and the shielding layers 3 and 12.
Since the portion of the substrate where the magnetoresistive elements 13 are formed is used for products as thin film magnetic heads after the DC resistance of each of the magnetoresistive elements 13 is set to the predetermined value, the work of removing smearing between the electrode layers 8 and the shielding layers 3 and 12 in each magnetoresistive element 3 must be carried out before products of thin film magnetic heads are manufactured.
However, with an excessively narrow gap, it is very difficult to appropriately remove smearing which occurs in narrow magnetic gap G1, thereby causing the problem of deteriorating the yield of thin film magnetic heads.
Particularly, a conventional element has a structure in which each of the electrode layer pairs 8 and 10 exposed from the ABS have a large width dimension T1, and thus smearing readily occurs in the electrode layers 8 and 10 in controlling the height as the gap is increasingly narrowed.
The present invention has been achieved for solving the above problems, and it is an object of the present invention to provide a thin film magnetic head in which the shape of electrode layers is improved for decreasing smearing between the electrode layers and shielding layers in controlling the height, thereby making adaptable to gap narrowing, and provide a substrate for forming the magnetic head thereon.
The present invention provides a thin film magnetic head comprising a lower shielding layer, a magnetoresistive element formed on the lower shielding layer with a lower gap layer provided therebetween and comprising a multilayer film exhibiting magnetoresistance, a pair of bias layers formed on both sides of the multilayer film, for applying a bias magnetic field to the multilayer film, and a pair of electrode layers formed on the bias layers to conduct to the multilayer film, and an upper shielding layer formed on the magnetoresistive element with an upper gap layer provided therebetween, wherein each of the electrode layers and the bias layers comprises a front end region with a predetermined length dimension from the ABS in the height direction, and a back end region formed in the height direction to extend from the boundary with the front end region in the track width direction.
In the above construction of the present invention, in each of the bias layers and the electrode layers, which are formed on both sides of the multilayer film exhibiting magnetoresistance, the width dimension of the portion exposed from the ABS can be decreased to a value smaller than conventional elements, thereby manufacturing a thin film magnetic head causing no smearing between the bias and electrode layers and shielding layers.
In the present invention, in the front end regions of each of the electrode layer pair and the bias layer pair, the width dimension of a portion exposed from the ABS is preferably not more than about ⅔ the width dimension of the lower shielding layer and/or the upper shielding layer.
In the present invention, in the front end region of each of the electrode layers and the bias layers, the width dimension of the portion exposed from the ABS is preferably not more than about {fraction (9/10)} the maximum width dimension of the back end region.
Furthermore, in the front end regions of each of the electrode layer pair and the bias layer pair, the width dimension of the portion exposed the ABS is preferably about 80 xcexcm or less.
In the present invention, in the front end regions of each of the electrode layer pair and the bias layer pair, the width dimension of the portion exposed from the ABS is appropriately set in relation to the width dimension of the shielding layers. Therefore, the occurrence of smearing can be properly prevented. Particularly, it was confirmed by the experiment described later that the above-mentioned numerical limits can decrease the rate of short circuits between the electrode layers and the shielding layers to 10% or less.
In the present invention, in the front end regions of each of the electrode layer pair and the bias layer pair, the width dimension of the portion exposed from the ABS is preferably not more than about xc2xc the width dimension of the lower shielding layer and/or the upper shielding layer. In the front end region of each of the electrode layers and the bias layers, the width dimension of the portion exposed from the ABS is preferably not more than ⅓ the maximum width dimension of the back end region. Furthermore, in the front end regions of each of the electrode layer pair and the bias layer pair, the width dimension of the portion exposed from the ABS is preferably not more than 30 xcexcm.
It was confirmed by the experiment described later that the above numerical limits can decrease the rate of short circuits between the electrode layers and the shielding layers to 5% or less.
In the present invention, the length dimension of the front end region in the height direction is preferably in the range of 0.5 xcexcm to 2.0 xcexcm.
In the present invention, assuming that a line extended from the outer edge of the front end region, or when the outer edge of the front end region has a curved line, a line tangent to the curved line at the center of the length thereof, is a first phantom line, and a line extended from the outer edge of the back end region, or when the outer edge of the back end region has a curved line, a line tangent to the curved line at the center of the length thereof, is a second phantom line, the inclination angle xcex1 of the first phantom line with respect to the height direction is preferably smaller than the inclination angle xcex2 of the second phantom line.
In the present invention, the first phantom line may be extended in parallel with the height direction, or the outer edge of the front end region may be linearly extended in the height direction while being extended in the track width direction.
The present invention provides a substrate comprising a magnetoresistive element for a thin film magnetic head, comprising a multilayer film exhibiting magnetoresistance, a pair of bias layers formed on both sides of the multilayer film, for applying a bias magnetic field to the multilayer film, and a pair of electrode layers formed on the bias layers to conduct to the multilayer film, and a magnetoresistive element for a monitor used for controlling the height and having the same construction of the magnetoresistive element for a thin film magnetic head, both of which elements are formed on a lower shielding layer with a lower gap layer provided therebetween; and an upper shielding layer formed on the magnetoresistive elements with an upper gap layer provided therebetween; wherein at least one of the magnetoresistive element for a thin film magnetic head and the magnetoresistive element for a monitor has the above-described structure.
A thin film magnetic head comprising a magnetoresistive element comprising a spin-valve film (a GMR element) is formed from a wafer, on which a plurality of magnetoresistive elements are formed, through various processes.
The exposed surface of the magnetoresistive element formed in the thin film magnetic head is referred to as xe2x80x9cABSxe2x80x9d so that the exposed ABS is opposed to a recording medium in reproduction of signals from the recording medium. The direction perpendicular to the ABS and apart from the recording medium opposed to the ABS is referred to as xe2x80x9cthe height directionxe2x80x9d. The length dimension of the magnetoresistive element in the height direction is a very important dimension for determining the DC resistance of the magnetoresistive element.
In order to set the length of the magnetoresistive element in the height direction to a predetermined value by grinding (height controlling) in relation to the DC resistance, a monitor element having the same construction as the magnetoresistive element is formed on the same line as the magnetoresistive element formed on the substrate so that the ABS-side surfaces of the magnetoresistive element and the monitor element are subjected to the height controlling process while measuring the DC resistance of the monitor element. When a predetermined resistance value is obtained, the height controlling process is finished. As a result, the magnetoresistive element has a length dimension in the height direction with which the predetermined resistance is obtained.
In the present invention, in order to comply with the demand for narrowing the gap with an increase in the recording density, each of the bias layers and the electrode layers which constitute the monitor element and/or the magnetoresistive element comprises a front end region and a back end region which is formed in the height direction to extend from the boundary with the front end region in the track width direction. Therefore, in the front end region, the width dimension of the portion exposed from the ABS can be decreased to a value smaller than conventional elements. In addition, on the back end side, the region where the bias layers and the electrode layers are formed can be maintained to the same level as conventional elements.
In the present invention, the width dimension of the front end region of each of the bias layers and the electrode layers can be set to a small value, thereby permitting the height controlling process while appropriately measuring the DC resistance of the monitor element with causing less smearing.
The substrate on which the thin film magnetic head is formed is finally cut for each magnetoresistive element to complete a thin film magnetic head. With the magnetoresistive element comprising the bias layers and the electrodes formed in the above-described form, smearing less occurs in a thin film magnetic head as a completed product, thereby manufacturing thin film magnetic heads with high yield.